This invention relates generally to turbine nozzle assemblies for gas turbine engines and more particularly to inner support structure for turbine nozzle assemblies.
A gas turbine engine includes a compressor that provides pressurized air to a combustor wherein the air is mixed with fuel and ignited for generating hot combustion gases. These gases flow downstream to one or more turbines that extract energy therefrom to power the compressor and provide useful work such as powering an aircraft in flight. Aircraft engines typically include a stationary turbine nozzle disposed at the outlet of the combustor for channeling combustion gases into the turbine rotor disposed downstream thereof. The turbine nozzle must direct the combustion gases in such a manner that the turbine blades can do work. Therefore, proper positioning of the turbine nozzle is needed for the turbine to produce optimal work. However, the turbine nozzle is subject to differential thermal expansion with adjoining components due to the highly heated combustion gases. This can lead to undesirable thermally induced stresses in the turbine nozzle.
Accordingly, turbine nozzle assemblies must be designed to accommodate the thermal loading. This includes mounting arrangements that allow the nozzles to freely expand circumferentially and radially while maintaining proper positioning. Turbine nozzles are typically segmented around the circumference thereof with each nozzle segment having one or more nozzle vanes. Suitable seals are provided between adjacent nozzle segments. Each segment is supported by a stationary nozzle support which allows limited relative movement of the nozzle segments to accommodate the differential thermal expansion and contraction of adjacent components. The nozzle support also supports the inner liner of the combustor, which is attached to the nozzle support by a number of bolts. During operation of the engine, the flow of combustion gases exerts an axially aft force on the nozzle segments to firmly press the nozzle segments against the nozzle support at their radially inner ends. The radially outer ends of the segments are pressed against a conventional shroud hanger disposed downstream therefrom. However, suitable means must be provided to hold the nozzle segments in place when the combustion gases do not provide sufficient axial force to firmly hold the nozzle segments in place.
In many conventional configurations, the inner band of a nozzle segment is directly bolted to the nozzle support. Such arrangements can create stresses in the nozzle segments and support due to differential thermal expansion and contraction. Furthermore, these designs use costly fasteners and bolted flanges and increase assembly and disassembly time.
In addition to supporting the nozzle segments and the combustor liner, the turbine nozzle assembly includes structure to supply cooling air to various areas of the turbine. Part of this structure includes a stationary air seal that is bolted to the aft end of the nozzle support. Air seals in conventional turbine nozzle assemblies must be removable in order to provide access to the bolts that attach the combustor liner to the nozzle assembly. This arrangement also increases the overall quantity and complexity of the hardware.
Accordingly, there is a need for a turbine nozzle assembly having support structure that accommodates differential thermal expansion and maintains proper nozzle position without the use of costly, time-consuming threaded fasteners.